Fix style in NUM_CIPHERS definition in cipher_wrap.c

Use brackets around `sizeof()` arguments as well as the entire macro.

Author: Hanno Becker

library/cipher_wrap.c

@@ -2266,7 +2266,8 @@ const mbedtls_cipher_definition_t mbedtls_cipher_definitions[] =
     { MBEDTLS_CIPHER_NONE, NULL }
 };
 
-#define NUM_CIPHERS sizeof mbedtls_cipher_definitions / sizeof mbedtls_cipher_definitions[0]
+#define NUM_CIPHERS ( sizeof(mbedtls_cipher_definitions) /      \
+                      sizeof(mbedtls_cipher_definitions[0]) )
 int mbedtls_cipher_supported[NUM_CIPHERS];
 
 #endif /* MBEDTLS_CIPHER_C */